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Date:	Fri, 03 Apr 2015 18:10:44 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Alexei Potashnik <alexei@...estorage.com>
Cc:	Joern Engel <joern@...estorage.com>,
	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org
Subject: Re: neigh use-after-free

On Fri, 2015-04-03 at 17:57 -0700, Alexei Potashnik wrote:

> 
> My understanding of the state when issue occurs is:
>  - neigh_destroy() has finished executing
>  - no timer for this neigh entry is pending or running
>     (which makes neigh_timer_handler behavior irrelevant)
>  - but kfree_rcu callback for the neigh entry has not executed yet
>  - at this point IP code finds the entry with __ipv4_neigh_lookup_noref
>     and starts operating on it.
> 

Right. So far no rule here seems to be violated.

As long as IP code finds a neighbor, it is allowed to use it.

Freeing of the neighbor should not happen before rcu grace period.

Problem is __neigh_event_send() is ignoring n->dead



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